1. Technical Field
The present invention relates to an ion implantation apparatus used for implanting ion species into semiconductor wafers or the like by irradiating ion beam, and in particular to an ion implantation apparatus shaping a beam shape by allowing the ion beam to pass through a through-hole of a component.
2. Related Art
At present, ion implantation apparatus is used for implanting ion species into semiconductor wafers. The ion implantation apparatus will be explained below, referring to FIG. 3. The ion implantation apparatus 100 illustrated herein is configured as having an ion gun 110, an aperture component 120, and a wafer holding unit 130 as essential constituents.
The ion gun 110 is supplied with ion species from an ion source (not shown), and emits it in a form of ion beam 115. The aperture component 120 is typically made by machining carbon or graphite, given as a flat-plate main component 121 having a slit like through-hole 122 formed therein.
The wafer holding unit 130 has a rotating stage 131 and a slider mechanism (not shown), wherein a plurality of silicon wafers 140, as target works, are held by the rotating stage 131. The rotating stage 131 allows thus-held plurality of silicon wafers 140 to revolve, and the slider mechanism allows the rotating stage 131 to move in a reciprocating manner typically upward and downward.
In thus-configured ion implantation apparatus 100, an ion beam 115 emitted from the ion gun 110 is allowed to pass through the through-hole 122 of the aperture component 120, during which the beam shape is shaped.
Thus-shaped ion beam 115 is irradiated sequentially to the plurality of silicon wafers 140 revolved by the wafer holding unit 130 and moved upward and downward, so that the ion species is uniformly implanted over the entire surface of the plurality of silicon wafers 140.
The aperture component 120 described in the above may be referred also to as resolving aperture, beam aperture, slit component and so forth, all of which being composed of a flat-plate component having a slit like through-hole 122 formed therein, as shown in FIG. 4.
At present, various proposals have been made on this sort of ion implantation apparatus (for example, Japanese Laid-Open Patent Publication Nos. H10-025178, H11-149898 and H11-283552).
Another proposal has been made on an ion implantation apparatus (not shown), in which at least surficial portions of various components disposed along the path of ion beam are formed using a high-purity silicon. In thus-configured ion implantation apparatus, particles possibly generated as foreign matter out from the components disposed along the path of ion beam should be composed of high-purity silicon, so that the silicon wafers may successfully be prevented from being polluted.
The above-described, high-purity silicon has been disclosed as being typically composed of amorphous silicon deposited on the surface of component by CVD (chemical vapor deposition), amorphous silicon deposited by sputtering, and silicon grown by epitaxial method (for example, Japanese Laid-Open Patent Publication No. H03-269940).
In the ion implantation apparatus 100 described in the above, as shown in FIG. 5, a gas 111 of ion species always stays around the ion beam 115, so that the ion species form a deposited film 116 typically on the inner surface of the through-hole 122 of the aperture component 120 over a long period of use.
The film 116 deposited typically on the inner surface of the through-hole 122 of the aperture component 120 may occasionally drop under irradiation by the ion beam 115 as shown in FIG. 6, and may be transferred as a foreign matter 117 towards the silicon wafers 140.
The silicon wafers 140 under such situation may have the foreign matter 117 deposited on the surfaces thereof, or may have damage on the surfaces thereof due to collision of the foreign matter 117, only to be abandoned anyway.
In particular for the case of large-current-type ion implantation apparatus (not shown), generally composed as a batch system affording a large number, as large as 13, of silicon wafers 140 set therein, occurrence of failure as described in the above may waste a large number of silicon wafers 140 at a time.
The foreign matter possibly generated from the components in the ion implantation apparatus described in Japanese Laid-Open Patent Publication No. 03-269940 might be composed of silicon, but an anticipation still remains in that the collision of the foreign matter may damage the surfaces of silicon wafers. Even if the damage could be avoidable, the silicon foreign matter adhered on the surfaces of the silicon wafers may be causative of failure in the succeeding semiconductor processes.
FIG. 7 and FIG. 8 show an exemplary case having a coated film 123 covering the inner surface of the through-hole 122 and portions therearound of the front surface and the back surface of the aperture component 120.
The coated film 123 is formed typically as a thermal-sprayed film of 100 μm or around, by thermal spraying of silicon 126, wherein the surface thereof is given as a porous rough surface having random irregularities of several micrometers or smaller.
Because the inner surface and therearound of the through-hole 122 of the aperture component 120 of the ion implantation apparatus 100 is covered with the porous coated film 123, the gas 111 of ion species steadily stays around the ion beams 115 may be adsorbed by the porous coated film 123 as shown in FIG. 7.
As a consequence, the ion species may be less likely to deposit typically on the inner surface of the through-hole 122 even after a long period of use, so that the failure of the silicon wafers 140 due to dropping and transfer of the deposited film 116 may be prevented to a desirable degree.
It was however found that, when the coated film 123 was formed by thermal spraying of particles 125 from outside of the through-hole 122, the thermal-sprayed film was formed at around the entrance of the through-hole 122 to a thickness of expected degree (300 μm, for example), whereas formed on the inner wall surface of the through-hole 122 only to a thickness approximately one-third (100 μm, for example) of the expected thickness (FIG. 9C).
This is because the minimum diameter of the through-hole 122 is only as small as ½ to ⅗ of length of the through-hole 122, and also because thermal spraying is available only at a very small angle of spraying of the particles 125 away from the inner wall surface (deep behind the entrance) of the through-hole 122 (FIG. 9B).
It was also found that the aperture component 120 shown in FIG. 9C, attached to the ion implantation apparatus 100 so as to allow the ion beam 115 to pass through the through-hole 122 (FIG. 9D), showed gradual decrease in thickness of the thermal-sprayed film at around the entrance of the through-hole 122 of the aperture component on the ion source side 127, and on the inner wall surface (deep behind the entrance) due to damage given by the ion beam 115 after the elapse of a predetermine length of time, and finally showed exhaustion of the thermal-sprayed film (FIG. 9E). It was found that the thermal-sprayed film remained only at around the exit of the through-hole of the aperture component on the wafer side 128, and that a non-aligned deposited film 124 composed of the ion species and the thermal-sprayed film was formed.